The primary goal of this project is to determine the role of a novel G protein alpha/o subunit in signaling mechanisms in the brain. G proteins mediate the effects of extracellular signals on intracellular signaling pathways. They are particularly important in brain where the effects of many neurotransmitters are mediated by G protein-coupled receptors. G/o is the most abundant heterotrimeric G protein in brain, comprising about 0.2%-1% of total particulate protein. There is a single mammalian gene for the alpha/o protein, which gives rise to multiple mRNAs encoding at least two different Goalpha proteins. However, at least three major Goalpha proteins have been purified from brain. Preliminary Results reported here show that the third major isoform (alpha/oc) is a mixture of two proteins derived from the protein expressed from the major alpha/o mRNA (alpha/o1), but modified at one or the other of two specific asparagine residues. These two asparagine residues are next to each other and near the C-terminus in a region of the protein involved in upstream receptor and downstream effector interactions. The proposed work will characterize the function, distribution and origin of these modified proteins based upon biochemical studies of purified and recombinant proteins. The Specific Aims are: (1) To determine the functional differences between the Goalpha isoforms. (2) To determine the localization and distribution of the Goapha proteins in neural tissues, cell lines and subcellular fractions. (3) To determine the mechanism underlying the origin of the alpha/oc isoforms. These Specific Aims are designed to test the hypotheses that alpha/oa is a precursor of the alpha/oc proteins, and that the rate of production of alpha/oc is dependent upon the activity of the G protein signaling system, resulting in an altered signaling pathway with new properties as a result of the production of alpha/oc. Such a molecular mechanism affecting a major brain signaling protein would likely be an important component of memory, neural plasticity or other related neuroadaptive processes.